This application is based on application No. 2000-160750 filed in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a high frequency package, a wiring board and a high frequency module, in which high frequency elements are loaded and high frequency signals having frequencies of 10 GHz or more are transmitted.
2. Description of the Related Art
In the recent highly information-driven society, utilization of radio waves for information transmission has been under study in which radio waves ranging from microwaves whose frequency range is 1-30 GHz to millimeter waves whose frequency range is 30-300 GHz are dealt with. Application systems using millimeter waves, for example, vehicle interval radars have been proposed.
As a structure of high frequency module adopted in such systems, the structure of a known multichip high frequency package, in which a plurality of high frequency elements are mounted on one substrate and hermetically sealed altogether by a case, is the mainstream.
A schematic sectional view of this known multichip high frequency package is shown in FIG. 5. A multichip high frequency package 31 comprises a dielectric substrate 32, a frame 33, a cap 34, and a plurality of high frequency elements 35 sealed within the package. Each of the high frequency elements 35 is connected with a high frequency line 36 formed on the surface of the dielectric substrate 32 by a wire bonding 37.
Such a multichip high frequency package needs to have a large size for arranging the necessary high frequency circuit within the package. As a result, this has a problem in the yield of hermetic sealing caused by camber of the substrate, deformation of the frame and the cap or the like.
In order to solve this problem, another kind of high frequency module has been considered. In this module, each high frequency element is separately packaged, hermetically sealed and mounted on a substrate so that the individual high frequency packages are connected with one another by a high frequency line on the wiring board.
However, in the case of such a high frequency module having high frequency packages each of which includes a high frequency element separately and is mounted on the wiring board, when the signal frequency is as high as 10 GHz or more, reflection of the high frequency signals becomes great in areas where the high frequency packages are connected with the wiring board. Loss in such areas is so great that it is hard to obtain the required performance, making it very difficult to use high frequency modules in this mode.
It is an object of the present invention to provide a high frequency package loaded with high frequency elements, a wiring board on which the high frequency packages are mounted, and a high frequency module with the high frequency packages incorporated thereinto having a structure capable of reducing loss of high frequency signals especially those having frequencies of 10 GHz or more.
After accumulating studies on the loss of signals in high frequency modules having high frequency packages that are loaded with high frequency elements and mounted on a wiring board, the present inventors focused on the fact that a transmission characteristic of signals transmitted from a terminal to the other terminal had the property of cyclically varying in relation to frequency, and have found out that loss of high frequency signals could be reduced by regulating the high frequency line between each set of terminals in the high frequency package and the wiring board such that the frequency of signals transmitted along the high frequency line corresponds to the frequency located at a peak part (where transmittance is large) of the cyclic variation curve of the transmission characteristic.
A high frequency package according to the present invention is characterized in that a transmission characteristic of signals (which is the same as the insertion loss and corresponds to S21 in S parameter) transmitted from an input terminal to an output terminal has the property of cyclically varying in relation to frequency, and that the frequency of signals transmitted along a high frequency line inside the high frequency package corresponds to that at a part of the cyclic variation curve of the transmission characteristic where transmittance is large.
The wiring board according to the present invention is one that has at least two high frequency packages mounted thereon, in which a transmission characteristic from one terminal portion to the other terminal portion on a high frequency line connecting the two high frequency packages has the property of cyclically varying in relation to frequency, and the frequency of signals transmitted along the high frequency line corresponds to that at a part of the cyclic variation curve of the transmission characteristic where transmittance is large.
In addition, according to the present invention, a high frequency module may be arranged such that the high frequency packages having the specific structure above are mounted on a wiring board that comprises a high frequency line formed on the surface of a dielectric substrate, and that at least two high frequency packages loaded with high frequency elements are mounted on the wiring board having the specific structure above.
Furthermore, the most desirable high frequency module according to the present invention is arranged such that the high frequency packages having the specific structure above in which transmission loss is reduced are mounted on the wiring board having the specific structure above in which transmission loss is reduced.
Generally, in a high frequency module in which a high frequency package is mounted on a wiring board, when the frequency becomes as high as 10 GHz or more, signals reflect in areas where the high frequency package is connected with the wiring board causing the loss thereof to be large. According to the present invention, however, the length of the high frequency line between the input terminal and the output terminal in the high frequency package and the length of the high frequency line between the high frequency packages connecting the high frequency packages on the wiring board are regulated, and the cycle of the frequency variation of the transmission characteristic in accordance with each length is adjusted such that the signal frequency is located at a peak part of the cyclic variation curve of the transmission characteristic, thereby reducing transmission loss in the high frequency package and the wiring board, and accordingly reducing transmission loss in the high frequency module comprising the high frequency packages mounted on the wiring board.
The peak part of the cyclic variation curve should preferably satisfy the following mathematical formula:
f1+{(f2xe2x88x92f1)/4}xe2x89xa6f0xe2x89xa6f2xe2x88x92{(f2xe2x88x92f1)/4}xe2x80x83xe2x80x83[Formula 1]
where f0 represents the frequency of signals transmitted along the high frequency line, f1 represents the frequency on the cyclic variation curve of the transmission characteristic at a part on the lower frequency side adjacent to f0, where transmittance is small, and f2 represents the frequency on the curve at a part on the higher frequency side adjacent to f0, where transmittance is small.
Moreover, it is preferable for the length of the high frequency line along which signals are transmitted to be (2n+1)xcex/4 (n: an integral number, xcex: wavelength of the signal frequency). This makes it possible to suppress transmittance loss due to the connection.
As discussed so far, the high frequency package, the wiring board and the high frequency module according to this invention are arranged such that the length of the high frequency line between the input terminal and the output terminal in the high frequency package and the length of the high frequency line connecting two high frequency packages on the wiring board are regulated in accordance with the wavelength of signals to be transmitted, and the frequency of the signals to be transmitted is controlled so as to be located at a peak part of the cyclic variation curve of the transmission characteristic, thereby bringing the reflection down to a minimum value and accordingly bringing the loss down to a minimum value. Reduction of loss due to the connection is therefore made possible, and a high frequency module that can deal with frequencies as high as 10 GHz or more can be realized in a mode in which high frequency packages are mounted on a wiring board.
Specific structural details of the present invention are hereinafter described referring to the appended drawings.